Machine-type-communication communications (abbreviated as MTC, also called Machine to Machine (M2M)) is a capability that enables the implementation of the “Internet of things” (abbreviated as IOT). It is defined as information exchange between a subscriber station (or a wireless communication device) and a server through a wireless communication network or between subscriber stations, which may be carried out without any human interaction. Several industry reports have scoped out huge potential for this MTC market. Given the huge potential, several wireless protocols backward compatible to current wireless communication standards for enabling MTC applications. The characteristics of MTC or JOT are that data is transmitted from MTC devices frequently or infrequently and with low data rate, such that long period operation can be achieved in low cost.
Use case model of MTC communications may include healthcare, secured access & surveillance, public safety, and remote maintenance & control, high priority access is necessary in order to communicate alarms, emergency situations or any other device states that require immediate attention. The future MTC networks can support many services such as industrial JOT, mobile commerce JOT, smart appliances JOT, healthcare JOT, and emergency JOT. Different IOTs or service applications have different service requirements. According to statistics from a wireless communication operator, there may be more than 30,000 MTC devices installed within the radio service coverage of one base station in urban area, or nearly 5,000 MTC device installed in a central urban area, while a normal base station is assumed to serve about 1,000 user equipments (UE).
Further, when a large amount of MTC devices simultaneously request to setup connection with the same base station, it may cause huge burden on the base station. On the other hand, due to the shared wireless medium, the aforementioned connection setup requests form MTC devices may further result in collisions, and after each collision, the MTC devices shall perform respectively random backoff processes for the next connection request transmission. When the collision situation is severe, the connection setup may be failed due to exceeding the pre-configured limit on connection setup request. For example, when the MTC device is required to transmit emergency message (which should be regarded with the highest priority) through the base station, the emergency message may be outdated due to the aforementioned collision and subsequent connection setup failure. Therefore, it is a major issue to design a prioritized random access process suitable for different priority accesses in a wireless communication system.